Thoughtless / careless citizens who flush their pharmaceuticals as their method of disposal. These same medications show up "downstream" in the hydrological cycle that all of us should have learned about in science classes.

EDCs (endocrine disrupting compounds)

For example, our EPA has been monitoring the upper end of our food chain -- fish -- representing the "canary in the mine", early warning. Apparently, male fish are showing up with female characteristics. Who would have known ? ! ! !